Properties of the glycolytic pathway: Identify the statement that is NOT true regarding glycolysis in typical cells under standard instructional assumptions.

Difficulty: Easy

Correct Answer: The pathway oxidizes two moles of NADH to NAD+ per mole of glucose

Explanation:


Introduction / Context:
Glycolysis is a central, ancient pathway converting glucose to pyruvate through ten enzyme-catalyzed steps. This item asks you to spot the incorrect statement among commonly taught characteristics.



Given Data / Assumptions:

  • Glycolysis occurs in the cytosol and can run anaerobically.
  • ATP is both consumed and produced within the pathway.
  • NAD+ is reduced to NADH during the glyceraldehyde-3-phosphate dehydrogenase step.


Concept / Approach:
Track electron flow: in glycolysis, NAD+ is reduced to NADH (it gains electrons). NADH may later be reoxidized to NAD+ via mitochondrial electron transport (aerobically) or by fermentation pathways (anaerobically). Glycolysis itself does not oxidize NADH; it generates it.



Step-by-Step Solution:
Confirm ATP generation by substrate-level phosphorylation at the phosphoglycerate kinase and pyruvate kinase steps. Confirm oxygen independence: no O2 is needed for the core ten reactions. Identify the false statement: “oxidizes NADH to NAD+.” In reality, glycolysis reduces NAD+ to NADH. Recognize that two ATP are invested (hexokinase and phosphofructokinase steps).


Verification / Alternative check:
Stoichiometry per glucose: invest 2 ATP; produce 4 ATP; net 2 ATP; produce 2 NADH; form 2 pyruvate.



Why Other Options Are Wrong:
Option a, b, d, and e are correct statements; e is valid because glycolysis functions in cells lacking mitochondria (for example, erythrocytes).



Common Pitfalls:
Confusing the role of fermentation (which reoxidizes NADH) with steps inside glycolysis.



Final Answer:
The pathway oxidizes two moles of NADH to NAD+ per mole of glucose.

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